Field of Invention
The present invention relates to a piezoelectric element, a piezoelectric actuator including the piezoelectric element, and a piezoelectric sensor, and a hard disk drive provided with the piezoelectric actuator and an ink-jet printer device. In particular, the piezoelectric element relates to a piezoelectric element including a piezoelectric layer.
Background Art
As for utilization of piezoelectric materials, instead of bulk piezoelectric materials, commercialization of a piezoelectric element by using a thin film piezoelectric material has proceeded. Examples include a gyro sensor, a shock sensor, and the like taking advantage of a piezoelectric effect, in which a force applied to a piezoelectric layer is converted to a voltage, and an actuator, an ink-jet print head, a speaker, a buzzer, a resonator, and the like taking advantage of an inverse piezoelectric effect, in which a piezoelectric layer is deformed when a voltage is applied to the piezoelectric layer.
In the case where a piezoelectric material is made into a thin film, miniaturization of an element becomes possible, applicable fields are expanded and, in addition, mass productivity increases because many elements can be produced on a substrate in one operation. Furthermore, there are many advantages in performances, for example, the sensitivity is improved in the case where a sensor is produced.
Piezoelectric constants d31 and e31 are mentioned as indicators of the use of piezoelectric materials. It is said that as the absolute values of these values increase, better piezoelectric effect and inverse piezoelectric effect are exhibited.
The reliability of the piezoelectric material tends to increase as the insulating property increases. A leakage current density is mentioned as the indicator to exhibit the insulating property. It can be said that as the leakage current density is low, the insulating property is high.
Also, in many cases, previously known piezoelectric materials typified by lead zirconate titanate (PZT) contains lead. Development of a piezoelectric material free from lead has been desired from the viewpoint of an environmental issue.
[PTL 1] Japanese Unexamined Patent Application Publication No. 2011-109037
[PTL 2] Japanese Unexamined Patent Application Publication No. 2009-200468
[NPL 1] S. H. Baek et al.: Science 334 (2011) 958
[NPL 2] X. Wu et al.: Ferroelectrics 367 (2008) 61